So for a non-woodworking project, I needed to melt copper in an effort to make bronze. I have a small electric foundry which I thought I could use. It turns out, the capacity is too small and it can only hold about half of what I need. So, in a very Morden/MacGuyver type of way, I decided to build a foundry.
First I needed a plan. I wasn’t planing on using this foundry often, so speed was more important than durability. I found Grant Thompson/King of Random’s plans for the mini foundry. In a later update he admits they are not the most durable thing, but he gives guidance on how to possibly extend their life. I’ll put links to the videos down below. As I go through the build, I will note the changes I made.
Casting the Foundry
The first thing I had to do was make the foundry. Using a 5 gallon bucket, I mixed up a 50-50 mix of playground sand and Plaster of Paris. I used a 2.5 quart plastic bucket with the handle removed as my scoop. I went with approximately 1.75 buckets of plaster and 1.75 buckets of sand. The dry goods were then mixed very well by hand. I then added 1.25 buckets of water. This is all according to the instruction video. Grant must be used to a drier climate than we have in Georgia. I ended up adding a little more sand and plaster to thicken the mix.
I lined a 10 quart galvanized steel bucket with coarse steel wool which had been unrolled. This will act as reinforcement and should extend the life of the foundry. Next the plaster mixture was poured over the wool. Try to keep the wool to the side and bottom. To form the hollow where the crucible will sit, insert the 2.5 quart plastic bucket in the center of the mixture. You will need to weigh it down with something. I filled it with water and set a brick on top, but if you have something solid I think it will work better. You want the top of the small bucket to be even with the top of the plaster.
Let the plaster dry for about an hour to an hour an a half. Then take a large pair of pliers and grasp the edge of the bucket in the center and try to ‘roll it up.’ The bucket should pop out and you should be left with a smooth void in the center.
Now we need to make a hole for air or torch, depending on what fuel source you use. Take a 1 3/8″ hole saw and drill a hole about 1/3rd of the way down the foundry. Angle the hole downward. You can see in this picture the hole with the torch (more on it later) inserted.
For the lid, Grant used a specific bucket. I did not have that type of bucket, but I did have an extra 5 gallon bucket. It turns out the bottom of the 5 gallon bucket is almost exactly the same size as the mouth of the foundry’s bucket. So I used that for the mold. It resulted in two issues which I will discuss in a bit.
The same 1 to 1 ratio of sand to plaster is used for the top. I just eyeballed it until I had 4-5″ of depth in the bucket-mold. Add water until the mix is a loose pancake batter consistency. Insert unrolled steel wool around the edges and make sure it gets fully covered in the mixture. Try to minimize the steel wool in the center. I just left it solid and drilled the center out with a 4″ hole saw later. My recommendation is that you use something to mold the center open instead (like I did during the foundry molding).
Now we need handles. After the mix has set just enough to hold them vertical, insert two 4″ U bolts that have a bar between them. Should look like this:
So, the issues. First the dry lid would not let go of the mold, so I had to cut the bucket up. If you are going to try to use this method, you may wish to consider using some type of release agent. Secondly, the lid is so close to the size of the top of the foundry, the loops of the handles on the foundry interfere with it seating properly. I can push it on without too much trouble, but I may end up removing the handle as a permanent fix. The final issue goes back to the vent hole in the center. I had difficulties with drilling through it with a hole saw because of the thickness. Hence my recommendation to use something to mold the opening into the casting.
When it comes to fuel sources there are two choices. One is propane, which I’ll go into detail below. The other is charcoal. Depending on the heats you are trying to achieve, charcoal is a perfectly valid option. If you use lump charcoal instead of briquettes, you can even reach over 2000 degrees. If you go this route, you’ll use a hair drier some piping to provide air through the hole in the side of the foundry. I did not go this route, so you will have to watch Grant’s videos for those instructions.
I went with propane. This is the more expensive way to go, but I felt it was more suited to how I would use it. Plus it would get to the temperatures I needed. The rough parts list:
I started with the nozzle. Take a hex head plug with a 1/4″ NPT male nipple on it and drill a 6 mm hole straight down through the center of the top. This needs to be a very straight hole, so use a drill press if you have one. Then tap threads into the hole using a 6 mm-1.00 tap. This will fit a .025″/6 mm MIG welder wire feed contact tip. Take a 1/4″ steel coupling and file four sides (at 90 degrees) flat. Screw the contact tip into the brass plug and the plug into the coupling. Use thread tape on all connections.
The next step involves a bit of variation from Grant’s video. He uses a steel 1.5″ to 1″ reducer coupling. I could not find that, so I had to reduce in two steps. Take the 1.5″ to 1.25″ reducer and file a flat spot on four sides, all at 90 degrees. Then drill a hole for the set screws. Grant uses a different size for his set screws, but I used the 6 mm size so I only had to buy one tap. This means I got slightly larger cap screws. Drill a 6 mm hole through each of the flat spots, tap the holes and insert the cap screws. These four screws are then used to hold the nozzle we build earlier straight and centered pointing out of the smaller end of the reducer.
If you managed to find the 1.5″ to 1″ reducer, you would just screw the six inch long, 1″ diameter pipe into this. Since I did not find one, I had to go to a 1.25″ threaded insert, into my next reducer then into the six inch pipe.
Theoretically you can do this without a regulator. I think that is a bad idea and will put a lot of stress on your components. Go to a local propane or plumbing supplier (not a big box store) and buy a regulator. They can also make an 8′ hose for you which will run between the regulator and the 45 degree elbow with a 3/8″ flare to 1/4″ male pipe. The 1/4″ end of the elbow will join one end of the 1/4″ NPT Female ball valve (Make sure the lever on the ball valve can be actuated without running into anything. Ideally you want it to turn away from the torch body). The other end of the ball valve will use the 1/4″ x 1/4″ NPT male fitting to join the nozzle we built earlier. Again, use thread tape on all connections. You should now have a completed torch which will fit into the hole in the side of the foundry.
To control airflow, cut a Pac-Man shape out of a tuna can lid. This can be slid over the pipe where it screws into the nozzle. Sliding it back and forth will adjust the amount of air the flame gets.
The completed foundry:
Buy one. Seriously. They are less than 20 bucks for decent sizes. I bought a #3-4KG clay graphite crucible from amazon for $19.95, then found one cheaper later. That size fits rather nicely in this foundry by the way.
You will need to season your crucible. This is basically heating it with borax until the borax turns liquid, then coating the interior of the crucible with the liquid. I did my test firing of the foundry at the same time I seasoned my crucible.
I have to admit, the the first firing did not go so well. It took forever to get up to temp, and I’m not sure it ever really got there. It ended up burning for two hours before the borax I was using to season the crucible started to turn liquid. I suspect this is because the plaster still had a bit of moisture to cook off combined with my inexperience at fuel/air ratios.
The next day I tried my first real smelting. I was trying to make leaded bronze from it’s component metals. The foundry came up to temp in about 20 minutes this time, melting the copper in the crucible and forming the bronze in under 30 minutes.
In all honesty, the first smelting was a failure for what I was trying to accomplish, but a success for having a working foundry. While the copper, tin, and other trace metals alloyed as expected, the lead proved immiscible in copper. I’ve talked it over with some folks and have ideas of what to try on my next attempt. In the mean time, here’s a video of the first pour.